The present invention relates to a bypass turbo-fan type turbojet engine thrust reverser. In such engines, a duct may be provided downstream of the fan to channel the so-called cold, bypass air exhausting flow from the fan. The duct consists of a fixed structure or fan nozzle having an inner surface which surrounds the engine proper and an outer wall, the upstream portion of which may be an extension of the surface of the portion of the cowling which surrounds the fan. The fan nozzle may channel both the bypass flow and the so-called hot, primary flow exhausting from the rear of the engine proper (in which case the hot and cold flows may be mixed or may channel only the bypass flow when so-called separate flows are involved.
As suggested above, a wall may fair the outside of the engine, that is, the outside of the casing or cowling enclosing the fan and the outside of the outer wall of the above described duct in order to minimize powerplant drag. This applies in particular to powerplants mounted on the outside of the aircraft, especially when these powerplants are attached under the wings or affixed to the rear of the fuselage.
The French patent application No. 96.09705 (FR-A2,752,017) published Feb. 6, 1998 describes an illustrative embodiment shown in FIG. 1 of the attached drawings of a thrust reverser fitted with scoop doors and associated with a bypass turbojet-engine.
This thrust reverser consists of a movable assembly and a fixed structure. The movable assembly is composed of hollow scoop type doors 3 that form movable components 2 and, in the forward-thrust mode, provide a surface which is contoured to form part of the exterior surface of the cowling. The fixed structure consists of an upstream portion 6 upstream of the doors 3, a downstream portion 7 downstream of the doors 3, and beams (not shown) connecting the upstream portion 6 to the downstream portion 7 and extending between the sides of the doors 3, the fixed structure also being part of the exterior cowling.
The doors 3 are located along a circumference of the cowling and are pivotable about an axis located in a downstream region of the doors by means of a pivot coupled to the circumferential sides of the doors and to the beams (not shown) which connect the downstream portion 7 to the upstream portion 6 of the cowling. The beams are situated on each side of the doors 3 along the door side walls connecting the outer surface or panel 4 of the doors 3 that constitutes a segment of the exterior cowling wall to the inner wall 5 constituting part of the outer wall of the bypass duct.
The fixed upstream portion 6 comprises a forward frame 8 which may support the means controlling the displacement of the doors 3 such as linear actuators. These means controlling the displacements of the doors 3 also may be situated at other locations on the periphery of the door 3 such as downstream at the door. In the latter case the downstream structure 7 of the fixed structure may support the control means.
When driven towards thrust reversed positions, the doors 3 pivot in such manner that the portion of the doors upstream of the pivots 9 more or less fully obstruct the duct while opening passages in the external cowling to allow channeling of the bypass flows 13 and 14 in a lateral or outward direction relative to the duct axis both in the conduit or exhaust passage 10 formed by the structure of the scoop door 3 and between the deflecting edge and the outside of the outer structure 4 of the door.
The downstream end of each door 3 moves in the vicinity of the outside of the external cowling. The doors' pivot angle is adjusted to allow passing the deflected flow and to substantially reduce, even suppress the forward thrust from this flow and to generate a counter-thrust by producing an upstream-deflected flow component.
Because the excursions of the doors are constrained by aerodynamically dimensioning the flow passages in the cross-sections cleared by the upstream portions of the doors and by the positions of the doors in the reversed-thrust mode, the above described thrust reverser has a protruding shape 12 downstream of and outside the forward frame 8. A more or less pronounced dead-air or stagnant air zone 11 is generally encountered in this area with conventional door designs that reduces the effective passage cross-section for the flow 14 while limiting the reverse angle of the flow 14 toward the front of the cowling. This dead air zone 11 effectively constitutes an aerodynamic plug reducing the effective cross-section of the deflected reversed flow stream.
The decrease in the effective passage cross-section of the thrust-reversal flow entails degradation in aerodynamic performance. Achieving an effective area and direction of the reversed flow stream would require repositioning the pivot 9 in the downstream direction and increasing the length of the door 3, thereby reducing the exhaust cross-section of the flow 13 of the scoop door because the aerodynamic flow lines must be more concentrated downstream of the cowling. Lengthening the door 3 also reduces its opening angle and hence reduces the clearance between the exhaust cross-section 15 of the conduit of door 3 and the downstream visor 16 which serves as a forwardly extending fairing of the exterior surface of rear fixed structure 7. Lastly, the angular declination of the door 3 in the thrust reversed mode will be less upon lengthening the door and thus the thrust-reversal flow will be given a smaller forward velocity component.
Known designs have been proposed to improve such thrust reverser performance. For example, U.S. Pat. No. 3,605,411 discloses a conventional thrust reverser door design using a baffle on the fixed structure upstream of the door. This baffle must project outside the cowling to act as a barrier against the thrust-reversal flow to prevent this flow from being re-ingested by the engine. This baffle furthermore must be operated independently of the door.
French patent document A 2,627,807 also discloses a conventional thrust reverser door design which includes an inside cavity which creates aerodynamic perturbations in the path of the forward-thrust flow. A lip is situated at the base of the door deflection edge to smooth part of the external flow and rotates to a position in the thrust-reversal flow stream to improve thrust-reversal performance.
French patent application 96.15256 also suggest specifically using vanes which are combined with conventional thrust reverser doors to improve aerodynamic performance. Mounting said vanes requires an open area that must be provided in the interior of the door.